Process for preparing batch materials for the manufacture of glass

ABSTRACT

The invention relates to a process for manufacturing compounds based on one or more silicates of alkali metals and/or of alkaline-earth metals, optionally in the form of mixed silicates that combine at least two of these elements, said process involving:
         (i) preferably a conversion reaction (1) in which halides of said alkali metals and/or of said rare earths and/or of said alkaline-earth metals are converted into the corresponding sulfates;   (iii) a conversion reaction (2) in which said sulfates together with silica are converted into the corresponding silicates, the heat supply needed for this conversion being provided, at least in part, by a combustion reaction (3) using a submerged burner or a plurality of submerged burners.

The invention relates to a process for preparing some of the materialsthat may be used to manufacture glass.

Within the context of the present invention, the term “batch materials”is understood to mean all materials, vitrifiable substances, naturalores or synthesized products, materials resulting from cullet-typerecycling, etc. that can be incorporated into the composition feeding aglass furnace. Likewise, the term “glass” is understood to mean glass inthe broad sense, that is to say encompassing any material with a glass,glass-ceramic or ceramic matrix. The term “manufacture” includes theindispensable step of melting the batch materials and possibly all thesubsequent/supplementary steps for the purpose of refining/conditioningthe molten glass for the purpose of its final forming operation,especially in the form of flat glass (glazing), hollow-ware (flasks,bottles), glass in the form of mineral (glass or rock) wool used for itsthermal or acoustic insulation properties, or even possibly glass in theform of yarns referred to as textile yarns used in reinforcement.

BACKGROUND OF THE INVENTION

The invention relates most particularly to the batch materials needed tomanufacture glasses having a significant content of alkali metals,especially sodium, for example glasses of the silica-soda-lime type usedto make flat glass. The batch material currently used most often forproviding sodium or potassium is sodium carbonate Na₂CO₃ or potassiumcarbonate K₂CO₃, which choice is not without its drawbacks since, on theone hand, this compound provides only sodium as constituent element ofthe glass, the entire carbonate part decomposing in the form ofevolution of CO₂ during melting. On the other hand, this is an expensivebatch material, compared with the others, since it is a syntheticproduct obtained by the Solvay process from sodium chloride and lime,which process involves a number of manufacturing steps and is quiteexpensive in terms of energy.

This is the reason why it has been proposed to use as sodium source nota carbonate but a silicate, possibly in the form of a mixed alkali metal(Na)/alkaline-earth metal (Ca) silicate prepared beforehand. The use ofthis type of intermediate product has the advantage of jointly providingseveral of the constituents of the glass, of eliminating thedecarbonatization phase and of reducing CO₂ emissions from the meltingfurnace. It also makes it possible to speed up the melting of the batchmaterials in their entirety and of favoring their homogenization duringmelting as indicated, for example, in the patents FR-1 211 098 and FR-1469 109. However, this approach poses the problem of the manufacture ofthis silicate.

A first method of synthesis was described in the patent WO-00/46161:this involves the conversion of a halide, for example NaCl, and silicainto a silicate at high temperature, the heat supply being provided bysubmerged burners.

Combustion by submerged burners is already known, for example from thepatents U.S. Pat. Nos. 3,627,504, 3,260,587 or 4,539,034, for meltingvitrifiable materials to make glass. To use this technology in a contextdifferent from the synthesis of silicates, and therefore upstream of theactual glass manufacture, indeed offers many advantages: this method ofcombustion causes, within the materials undergoing reaction, strongturbulence and vigorous convection motion around the gas jets or flamesfrom the submerged burners. This promotes very effective stirring of thereactants. Furthermore, submerged burners provide the heat directly atthe point where it is needed, into the mass of the products undergoingreaction. It is also an environmentally friendly method of combustion.

For further details about the various reactions involved, reference maybe made to the aforementioned patent WO-00/46161.

Direct conversion of NaCl and silica carried out in this way istherefore very attractive for more than one reason. However, this directconversion has proved to be ill suited to implementation on a largescale.

The object of the invention is therefore to develop another type ofsilicate manufacture, which can retain the advantages of the techniquedescribed above, while being easier to use on an industrial scale.Secondarily, it will be attempted to make this novel type of manufactureas environmentally friendly as possible and to take intoaccount/utilize, to the best, all the reaction products involved otherthan the silicates, the manufacture of the silicates remaining theprimary objective of the present invention.

BRIEF SUMMARY OF THE INVENTION

The subject of the invention is firstly a process for manufacturingcompounds based on one or more silicates of alkali metals, such as Na, Kand/or of alkaline-earth metals, such as Ca, Mg, and/or of rare earths,such as Ce, optionally in the form of mixed silicates that combine atleast two of these elements. This process involves:

(i) a conversion reaction (1) in which halides, especially chlorides, ofsaid alkali metals and/or of said alkaline-earth metals and/or of saidrare earths are converted into the corresponding sulfates;

(ii) a conversion reaction (2) in which said sulfates together withsilica are converted into the corresponding silicates, the heat supplyneeded for this conversion being provided, at least in part, by acombustion reaction (3) using a submerged burner or a plurality ofsubmerged burners.

The process according to the invention may also comprise only step (ii)according to reaction (2).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a preferred method of implementing the processaccording to the invention, operating in feedback mode.

DETAILED DESCRIPTION OF THE INVENTION

The term “silica” is understood here to mean any compound containingpredominantly silica (silicon oxide) SiO₂, even if it may also containother elements and other minority compounds, this being mostparticularly the case when natural materials of the sand type are used.

The term “submerged burners” is understood here to mean burnersconfigured so that the “flames” that they generate or the combustiongases emanating from these flames develop in the reactor where theconversion takes place, within the very mass of the materials beingconverted. Generally speaking, the burners are placed so as to be flushwith or slightly proud of the sidewalls or of the floor of the reactorused (the term “flames” is used here, even though they are not strictlyspeaking the same “flames” as those produced by crown burners, for thesake of simplicity).

The process described above is an improvement to the process describedin the patent WO-00/46161, in the sense that it splits into two separatesteps the overall reaction involving a halide (such as NaCl) and silicato make a silicate. In the present invention, there is thus anintermediate step consisting in manufacturing a sulfate. The industrialfeasibility is greatly improved thereby: it thus avoids having tothermally “break down” an NaCl-type halide at very high temperature,which would cause the NaCl to undergo a certain amount of volatilizationin the furnace where the reaction with the silica takes place. Incontrast, in the invention, step (1) of converting the halide into asulfate is easier to carry out and can take place at a relatively lowertemperature and under operating conditions already well controlled inthe chemical industry. Step (2) of converting the sulfate into asilicate by submerged burners makes it possible to obtain the desiredproduct with all the advantages of submerged burners mentioned in thepreamble of the present application.

To illustrate these two steps, for the purpose of manufacturing sodiumsilicate, the invention therefore proposes in particular the followingsuccessive steps:2NaCl+H₂SO₄→Na₂SO₄+2HCl  (i)Na₂SO₄ +xSiO₂→(SiO₂)_(x)—Na₂O+SO₂/SO₃  (ii)

For this second reaction, the value of x may vary—one example isespecially x=2.

The present text will later return to the beneficiation/utilization ofthe reactants/reaction products involved in these reactions, other thanNaCl, SiO₂ and the silicate (SiO₂)_(x)—Na₂O.

The effectiveness of the burners in all aspects (quality of the mixing,excellent heat transfer) means that the conversion according to reaction(2) is greatly favored, and is so without there being a need to attainextremely high temperatures.

Another advantage of submerged burners is the following: they allow theintroduction of liquid/solid fuels in the same way as the vitrifiablebatch materials. This consequently results in the obtaining of highredox levels of the molten silicate, this being favorable to the sulfatedecomposition reaction.

The chosen oxidizer for feeding the submerged burner(s) in reaction (2)may simply be air. However, it is preferential to use an oxidizer in theform of oxygen-enriched air, and even an oxidizer substantially in theform of oxygen alone. A high oxygen concentration is advantageous forvarious reasons: the volume of the combustion smoke is thus reduced,this being favorable from the energy standpoint and avoids any risk ofexcessive fluidization of the materials undergoing the reaction, thatmay cause splashing against the superstructures or the roof of thereactor where the conversion takes place. Furthermore, the “flames”obtained are shorter and more emissive, thereby allowing their energy tobe transferred more rapidly to the materials undergoingmelting/conversion.

As regards the choice of fuel for the submerged burner(s), threeapproaches are possible, as alternatives or in combination: it ispossible to choose a liquid fuel, a gaseous fuel or a fuel in solidform.

If it is at least partly in gaseous form, it may feed the submergedburners directly. If it is in liquid or solid form, it may be broughtclose to the submerged burners.

As gaseous fuel, mention may be made of natural gas (predominantlymethane), propane, hydrogen or any other hydrocarbon-based compoundand/or sulfur-based.

As solid or liquid fuel, mention may be made of any compoundpredominantly in carbon-based and/or hydrocarbon-based and/orsulfur-based form (including sulfur and carbon): as in the previouscase, these may be byproducts of the oil industry (heavy fuel oil,asphalt). They may be polymer-based materials that can thus be recycled(any plastics, tires, etc.), and even hydrocarbon-contaminated sand,which will also provide both the silica and the fuel, which is aningenious way of handling the problem of decontaminating beaches afteran oil spillage for example.

In fact, one particularly novel feature of the present invention is thatit is possible to use, if so desired, sulfur-containing fuels, or evenpure sulfur. There are traces of sulfur in all vulcanized polymers(tires) and sulfur is also found in byproducts of the oil industry, andthe invention allows them to be beneficially utilized: this is becausethe sulfur contained in the fuel provided for carrying out combustionreaction 3 will be oxidized. Now, as is known in the chemical/oilindustry, these sulfur oxides (SO₂ and/or SO₃) may be converted tosulfuric acid, by recovering them from the smoke and treating themappropriately. There are therefore two choices (alternative orcumulative in fact, especially depending on the quantity of H₂SO₄manufactured, which depends intimately on the chosen S content of thefuel), namely either the H₂SO₄ is utilized, as a reactant widely used inthe chemical industry, independently of the process according to theinvention, or it is reused in the process of the invention. This isbecause reaction (1) of converting the halides into sulfatesadvantageously uses sulfuric acid: this is therefore a “feedback”process in which the combustion product of reaction (2), once converted,is used as reactant in reaction (1).

There is another way, as an alternative to or in combination with theprevious one, of manufacturing H₂SO₄ from the process according to theinvention: reaction (2) of converting sulfate to silicate itselfproduces sulfur oxides SO₂ and/or SO₃. Here again, these sulfur oxidesmay therefore be recovered and made to undergo a conversion reaction,converting them to sulfuric acid. As in the previous case, this sulfuricacid may be reused as reactant in reaction (1) and/or it may be utilizedas a reactant for the chemical industry.

As a result, if the fuel contains a significant amount of sulfur, thesetwo reactions of converting sulfur oxides to sulfuric acid may producemore, and even significantly more, sulfuric acid than is needed forreaction (1) of converting the halides to sulfates, resulting in thebeneficiation of the process according to the invention in its entirety.

There is another reaction product in the process of the invention thatcan be utilized, especially in the chemical industry, this beinghydrochloric acid HCl, manufactured during reaction (1) of convertingthe halides to sulfates, when the halide in question is a chloride ofthe NaCl type.

Of course, it may be treated as an effluent, that can be neutralizedwith calcium carbonate CaCO₃, which amounts to manufacturing CaCl₂, thatcan be used for example for freeing roads from snow. HCl may also beconsidered as a base chemical widely used in the chemical industry (justlike H₂SO₄) and the HCl can be extracted from the smoke in order to setup an industrial HCl production line. It is therefore beneficial toinstall the plant for carrying out this reaction (1) on the chemicalindustry site that requires this type of chlorinated product.

A first outlet for the silicates manufactured according to the inventionis in the glass industry: they may substitute, at least in part, for theconventional batch materials that provide alkali metals or rare earths,with, particularly as regards sodium, at least partial substitution ofNa₂CO₃ with Na₂O—(SiO₂)_(x). The silicates of the invention cantherefore be employed for feeding a glass furnace.

It may be necessary for the silicate formed according to the inventionto be made to undergo a granulation-type treatment step before it isintroduced into the glass furnace. The glass furnace may be ofconventional design (for example, an electric melting furnace usingsubmerged electrodes, a crown-fired furnace operating with lateralregenerators, a horseshoe-fired furnace and any type of furnace known inthe glass industry thus including submerged-burner furnaces), possiblywith a design and an operating method that are slightly modified so asto be suitable for a melting process with no carbonate or with lesscarbonate than for standard melting operations.

It should be noted that certain silicates other than sodium silicate arealso very useful to manufacture according to the invention. Thus, theinvention allows potassium silicate to be manufactured from KCl, whichis, at least economically, very advantageous as batch materialcontaining Si and K for the manufacture of what is referred to as“mixed-alkali” glass, that is to say glass containing both Na and K.Such glass is used especially for producing tactile screens, glass fortelevision screens and glass for plasma display panels.

Likewise, the invention allows more economical manufacture of specialglasses containing additives, for which chlorides are less expensivethan oxides. This is the case with rare earths such as cerium—thepresence of cerium oxide giving the glasses UV-screening properties—andrare earths of this type are also found in the composition of specialglasses of high elastic modulus for hard disks. The invention thus makesit possible to have a batch material containing Si and Ce, namely ceriumsilicate, for a moderate cost.

A second outlet for the silicates manufactured according to theinvention (apart from those used as batch materials for a glassfurnace), more particularly sodium silicate, is in the detergentsindustry, sodium silicate frequently being incorporated into thecomposition of washing powders/detergents.

A third outlet for the silicates (and possibly the chlorinatedderivatives) formed according to the invention is in the preparation ofspecial silicas commonly referred to as “precipitated silicas” that areincorporated for example in the composition of concretes. This isbecause the silicates formed according to the invention may undergo acidattack, advantageously by sulfuric acid, so as to precipitate silica inthe form of particles having a particular particle size: the intendedparticle size is generally nanometric (1 to 100 nm of example).

To carry out reaction (1) of converting the halides to sulfates, areactor known in the chemical industry by the name Mannheim furnace maybe used.

To carry out reaction (2) of converting the sulfates to silicates, it ispossible to use, as described in the patent WO-00/46161, a reactorfitted with one or more submerged burners and with at least one means ofintroducing the silica and/or the sulfates below the level of the moltenmaterials, especially in the form of one or more feed-screw batchchargers. Preferably, the same applies in the case of the solid orliquid fuels possibly used, such as the carbon-based orhydrocarbon-based and/or sulfur-based compounds (including sulfur andcarbon) mentioned above. It is thus possible to introduce, directly intothe mass of products undergoing melting/reaction, at least those of thestarting reactants that can vaporize before having the time to react.

To optimize the entire process from the energy standpoint, the heat maybe recovered from the smoke output by the submerged-burner reactor usedfor reaction (2) and used to contribute to the heat supply needed forreaction (1) in the Mannheim-type furnace.

The process according to the invention described above therefore hasmany advantages, among which:

-   -   a reduction in CO₂ emissions in glass furnaces which completely        or partly substitute sodium carbonate with sodium silicate—these        furnaces consume less energy since the decarbonatization        reactions are reduced or eliminated;    -   beneficiation of the halogen of the starting halide, especially        in HCl form when it is a chloride;    -   the possibility of turning the process into a feedback process,        with the H₂SO₄ byproduct manufactured being reused; and    -   the possibility of utilizing sulfur-based derivatives as fuel.

The invention will be explained in detail below with the aid ofnonlimiting examples and with the aid of FIG. 1:

-   -   FIG. 1: a diagram of a preferred method of implementing the        process according to the invention, operating in feedback mode.

The two examples according to the invention both relate to themanufacture of sodium silicate from sodium chloride and sulfuric acid,according to the method of implementation illustrated in FIG. 1.

Let us now explain the details of the reaction process in terms of threemajor steps, each represented in the form of a feedback loop in FIG. 1:the purpose of the two examples is to manufacture 1000 kg of sodiumsilicate of formula Na₂O—(SiO₂)₂, i.e. 5489 mol. It will be consideredthat the yields of the reactions involved are 100%.

1—Synthesis of Sodium Sulfate

2 NaCl + H₂SO₄ → Na₂SO₄ + 2 HCl quantity in 2 × 5489 5489 5489 2 × 5489moles quantity in kg 642 538 779 401

This step is carried out in a Mannheim furnace in a known manner.

2—Synthesis of Sodium Silicate with Submerged Burner

Na₂SO₄ + 2 SiO₂ → Na₂O—(SiO₂)₂ + SO₂/SO₃ quantity 5489 2 × 5489 54895489 in moles quantity 779 660 1000 in kg

This synthesis is carried out in a submerged-burner furnace, like thatdescribed in the patent WO-00/46161.

3—Combustion Reaction Providing the Energy Needed for Synthesizing theSilicate (Estimated Here to be 2042 kWh/tonne of Silicate)

For a fuel containing carbon-based chains, of standard formula CH_(x),and sulfur, the combustion reactions are:CH_(x)+(1+x/4)O₂→CO₂ +x/2H₂OS+O₂→SO₂  (3)

Depending on the sulfur content of the fuel, in the combustion reactiona greater or lesser amount of SO₂ is released into the smoke which willbe added to the SO_(x) produced by the silicate synthesis itself. Thenumber of moles of SO₂ produced by the combustion is denoted “y”.

4 and 4′—Conversion of the Sulfur Oxides into Sulfuric Acid

SO₂/SO₃ → H₂SO₄ quantity in moles 5489 + y 5489 + y

5489 mol of H₂SO₄ are reintroduced into the sodium sulfate synthesis(1). The “y” moles remaining can be utilized outside this synthesisloop.

EXAMPLE 1

This example uses for step (3) fuel 100% in sulfur form (comingespecially from the desulfurization of oil refinery products).

Its net calorific value (NCV) is 2584 kWh/tonne of sulfur.

Reaction (2) requires 2042 kWh, i.e. 790 kg of sulfur (24688 mol of S).

Combustion of this sulfur produces y (=24688) moles of SO₂.

Apart from the 5489 mol self-feeding the feedback loop with H₂SO₄, afurther 24688 mol of H₂SO₄ are therefore obtained, i.e. 2420 kg that canbe utilized outside the feedback loop.

EXAMPLE 2

This example uses for step (3) a fuel in the form of a No. 2 heavy fueloil containing 4% sulfur.

Its NCV is about 10930 kWh/t. Therefore 187 kg of this fuel oil isneeded to produce one tonne of silicate.

7.5 kg of sulfur coming from this fuel oil, i.e. 234 mol, will thereforebe burnt, releasing y (=234) moles of SO₂.

234 mol, i.e. 23 kg of H₂SO₄ are therefore obtained that can be utilizedoutside the feedback loop.

It may therefore be seen that the excess sulfuric acid that can beobtained over that needed for reaction (1) varies greatly depending onthe choice of fuel. All the intermediate solutions, with the combinationof fuel oil and sulfur, or else the use of vulcanized tires, arepossible, thereby allowing the best adjustment of the combustion (3)depending on the type of fuel most available and/or on the amount ofsulfuric acid that it is desired to produce.

The present application is the U.S. counterpart of PCT/FR02/03398 (WO03/031357), filed on Oct. 4, 2002, the text of which is incorporated byreference and claims the priority of the French application No. 01/13021filed Oct. 8, 2001, the text of which is incorporated by reference.

1. A process for manufacturing compounds based on one or more silicatesof alkali metals, and/or of alkaline-earth metals, and/or of rareearths, said process involving a conversion reaction (1) in whichhalides of alkali metals and/or of rare earths and/or of alkaline-earthmetals are converted into the corresponding sulfates in a first reactor,and a conversion reaction (2) in which the sulfates of alkali metalsand/or of rare earths and/or of alkaline-earth metals are converted intothe corresponding silicates in a second reactor, wherein the heat supplyneeded for converting the sulfates into the silicates is provided, atleast in part, by a combustion reaction (3) using a submerged burner ora plurality of submerged burners, wherein sulfur oxides obtained duringconversion reaction (2) are recovered and the sulfur oxides undergo areaction (4′) to convert them into sulfuric acid, and wherein thesulfuric acid is used in reaction (1).
 2. The process as claimed inclaim 1, where in in combustion reaction (3), the at least one submergedburner is fed with at least one fuel in gaseous form.
 3. The process asclaimed in claim 2, where in the sulfur oxides possibly obtained byoxidation of sulfur-based compounds during combustion reaction (3) arerecovered and in that they are made to undergo a reaction (4) to convertthem into sulfuric acid.
 4. The process as claimed in claim 3, where inreaction (1) of converting the halides into sulfates is carried out withsulfuric acid, at least some of this sulfuric acid coming from reaction(4) of converting into sulfuric acid the sulfur oxides coming fromcombustion reaction (3) and/or from reaction (4′) of converting, intosulfuric acid, the sulfur oxides coming from reaction (2) of convertingthe sulfates into silicates.
 5. The process as claimed in claim 4, wherein reactions (4) and (4′) of converting the sulfur oxides into sulfuricacid produce more sulfuric acid than is needed for reaction (1) ofconverting the halides into sulfates.
 6. The process as claimed in claim1, where in in combustion reaction (3), at least one type ofsulfur-based fuel in liquid or solid form is brought close to saidsubmerged burner(s).
 7. The process as claimed in claim 1, wherein itmanufactures sodium silicate by: {circle around (1)}—conversion of NaClby H₂SO₄ into Na₂SO₄, together with HCl that can be utilized, {circlearound (2)}—conversion of the Na₂SO₄ into (SiO₂)_(x)—Na₂O by silica withheat supply using submerged burners.
 8. The process as claimed in claim1, where in the heat of the smoke of the submerged burner reactor usedfor reaction (2) is recovered and used to contribute to the heat supplyneeded for reaction (1).
 9. The process as claimed in claim 8, where inthe reaction (1) takes place in a Mannheim furnace.
 10. The process asclaimed in claim 8, where in the sulfur oxides obtained in the smokesare recovered and converted into sulfuric acid.
 11. The process asclaimed in claim 1, where in batch materials for the manufacture ofglass, raw materials for the manufacture of detergents, or raw materialsfor the manufacture of precipitated silica are prepared.
 12. The processas claimed in claim 1, where in the fuel for combustion reaction (3)comprises sulfur-based and/or hydrocarbon-based and/or carbon-basedderivatives of the oil industry byproduct type.
 13. The process asclaimed in claim 1, where in reaction (1) of converting the halides intosulfates is carried out with sulfuric acid and at least some of thissulfuric acid comes from reaction (4′) of converting, into sulfuricacid, the sulfur oxides coming from reaction (2) of converting thesulfates into silicates.
 14. The process as claimed in claim 1, where inconversion reaction (1) comprises converting at least one alkali halideinto the corresponding sulfate.
 15. The process as claimed in claim 14,where the alkali halide is selected from the group consisting of NaCl,KCl, and mixtures thereof.
 16. The process as claimed in claim 1, wherein conversion reaction (1) comprises converting at least one alkalineearth metal halide into the corresponding sulfate.
 17. The process asclaimed in claim 16, where the alkaline earth metal halide is selectedfrom the group consisting of CaCl₂, MgCl₂, and mixtures thereof.